1. Field of the Invention
The invention relates to a filling level transmitter having a sound-conducting tube and a filling level sensor with an ultrasonic transceiver and sensor electronics.
2. Related Art
Such filling level transmitters with an ultrasonic transceiver that generates and outputs ultrasonic waves and receives reflected ultrasonic waves are used, for example, to measure filling levels in fuel containers of motor vehicles and are therefore known.
When determining a filling level by ultrasound, in the first instance the variable measurement signal is problematical owing solely to changing measurement conditions such as, for example, the temperature or the measurement medium. For this purpose it is known to provide a reference measurement at a reference reflector in order to eliminate influence of changed measurement conditions. Owing to assembly tolerances, calibration must be carried out before the filling level transmitter is put into service. In addition, the reference measured section with the reference reflector is arranged in the vicinity of the actual measured section for the filling level and therefore separately, as a result of which additional installation space is required. On the other hand, an ultrasonic transceiver has, owing to the principle, a dead section that lies directly in front of the transceiver and in which reliable measurement is not possible. This dead section is produced as a result of the fact that the sound pulse which is emitted generates a certain amount of reverberation in the transceiver, which has to largely decay before an echo signal can be detected cleanly.